123 Pregnancy and calving rates in lactating Bos indicus × Bos taurus dairy recipient cows synchronized with two protocols with lengthened proestrus

An experiment was designed to evaluate pregnancy rates to embryo transfer (P/ET), pregnancy losses, and calving rates in lactating Bos indicus × Bos taurus recipient cows synchronized with an estradiol-based (J-Synch) or a GnRH-based (Web-Synch) protocol with lengthened proestrus. Gyr × Jersey lactating cows (n = 2131) were randomly allocated into one of 2 treatment groups. Cows in both groups were 55.0 ± 12.0 days in milk, had a CL or at least one follicle >8 mm in diameter (determined by ultrasonography), had a body condition score of 2.5–3.5 (1–5 scale), and were managed in a confinement system. On Day −6, cows in the J-Synch group (n = 1125) received 2 mg of estradiol benzoate (Calier) intramuscularly (i.m.) and an intravaginal device containing 1.2 g of progesterone (P4, Pluselar, Calier). On Day 0, P4 devices were removed, and all cows received 150 µg of d-cloprostenol (PGF, Veteglan, Calier) and 400 IU eCG i.m. (Vetegon, Calier). Cows in the Web-Synch group (n = 1006) were treated with PGF and a P4 device on Day −11; 10 µg of buserelin (GnRH, Pluserelina, Calier) on Day −6; and P4 device removal, PGF, and eCG on Day 0. Cows in both groups were observed for estrus signs at 72 h after device removal and those detected in estrus were examined by ultrasonography (Mindray M6 Vet) at the time of embryo transfer, 7 days after estrus (i.e. Day 19). Recipients with a CL >16 mm in diameter received grade 1 in vitro-produced blastocysts by nonsurgical transfer. Pregnancy was determined by ultrasonography at 30 and 90 days of gestation, and cows were then followed until parturition to determine calving rates. Data were analyzed using the GLM mixed procedure for binary data with a logit link (InfoStat, Di Rienzo et al. 2020). Recipients in the Web-Synch group had greater P/ET and calving rates than those in the J-Synch group (Table 1). Estrus and utilization rates and pregnancy losses did not differ among groups. In conclusion, the Web-Synch protocol seems to be more appropriate for lactating Bos indicus × Bos taurus recipients than the J-Synch protocol.